ASME-Landmark:John Penn & Sons Oscillating Steam Engine

The oscillating steam engine, built by John Penn & Sons, is located aboard the famed paddle steamer Diesbar, the second oldest of a fleet of nine paddle steamers in Dresden. What makes the Diesbar unique is its coal fueled engine and single deck design. The John Penn and Sons engine that runs the steamer is the oldest operational marine steam engine in the world. It has been in operation for over 175 years.

Built in 1841 by John Penn & Sons of Greenwich, England, the Diesbar's engine is a two-cylinder oscillating steam engine. The oscillatory feature allows for the incorporation of fewer parts in comparison with other steam engines of the era. This ultimately cut down on total material and helped to address two major engine design issues that plagued the time period, size and weight.

The John Penn engine is put into motion when steam from the boiler enters the cylinders of the engine. The steam enters the cylinders through the outboard trunnions and exhausts through the inboard ones. The third cylinder is fixed and is used to maintain a partial vacuum in the condenser. The crankshaft then turns two paddles with feathering blades, which turn twice as fast as fixed, radial blades and thus are twice as efficient.

While this particular John Penn & Sons engine has resided above the Diesbar for more than 130 years, it was originally aboard the Bohemia, starting in 1841, and then the Stadt Meissen in 1857. The John Penn engine was both a unique design and major contributor to early steam engineering. See ASME website for more information